The development of new forms of therapeutics which use macromolecules such as proteins or nucleic acids as therapeutic agents has created a need to develop new and effective means of delivering such molecules to their appropriate cellular targets. Therapeutics based on either the use of specific polypeptide growth factors or specific genes to replace or supplement absent or defective genes are examples of therapeutics which may require such new delivery systems.
Gene therapy has become an increasingly important mode of treating various diseases. The potential for providing effective treatments, and even cures, has stimulated an intense effort to apply this technology to diseases for which there have been only limited effective treatments. Recent progress in this area has indicated that gene therapy may have a significant impact not only on the treatment of single gene disorders, but also on other more complex diseases such as cancer. Gene therapy agents include expressible gene constructs but also RNA interference agents (RNAi). There has recently been a great deal of interest in the use of RNAi for basic research purposes and for the development of therapeutics to treat, e.g., disorders and/or diseases associated with unwanted or aberrant gene expression.
Success of a gene therapy protocol largely depends upon the vehicle used to deliver the gene. A variety of means exist to introduce a gene inside the cell including physical means such as microinjection (Capecchi, M. R. Cell (1980) 22:479-485), electroporation (Pacqereau, L. et al. Anal. Biochem. (1992) 204:147-151) and particle bombardment (Yang, N.-S. et al. Proc. Natl. Acad. Sci. USA (1990) 87:9568-9572)), biological means such as viruses (Ferry, N. et al. Proc. Natl. Acad. Sci. (1991) 88:8377-8381) and chemical means such as calcium phosphate (Wiegler, M. et al. Cell (1977) 11:223-232), DEAE dextran (Ishikawa, Y. et al. Nucl. Acid Res. (1992) 20:4367-4370), polylysine (Wu, G. Y. et al. J. Biol. Chem. (1988) 263:4429-4432) and cationic liposomes (Felgner, P. L. et al. Proc. Natl. Acad. Sci. (1987) 84:7413-7417)). Clinical application of such therapies depends not only on the efficacy of new delivery systems but also on their safety and on the ease with which the technologies underlying these systems can be adapted for large scale pharmaceutical production, storage, and distribution of the therapeutic formulations. Thus, an ideal vehicle for the delivery of exogenous agents into cells and tissues should be highly efficient in therapeutic agent delivery, safe to use, easy to produce in large quantity and have sufficient stability to be practicable as a pharmaceutical.
Accordingly a need exists for new and practical ways of making reagents suitable for introducing therapeutic agents into cells, in vitro and in vivo, and in particular, for use in developing human therapeutics.